This invention relates to an image-sensing apparatus using solid-state image-sensing devices, and more particularly to an image-sensing apparatus provided with an improved high voltage generating circuit for applying a bias voltage to the solid-state image-sensing devices.
In an image-sensing apparatus, an image-sensing device driving circuit, a signal processing circuit and a high voltage generating circuit are necessary. The driving circuit supplies timing pulses to solid-state image-sensing devices which, in turn, sense images, store charges introduced corresponding to the sensed images, and read such charges so as to produce electric signals. The signal processing circuit functions to receive and process the thus obtained signals so as to produce output signals. The high voltage generating circuit generates and supplies a bias voltage higher than the power source voltage of the apparatus to the solid-state image-sensing devices.
Specifically, in an image-sensing apparatus using solid-state image-sensing devices, the charge is transferred from a charge transferring section disposed on a semiconductor substrate, and stored within a floating diffusion region. The charge stored within the floating diffusion region is output from an output terminal as an output signal, however, in this case, a high DC bias voltage higher than the power source voltage is required. The high DC bias voltage is generated by a high voltage generating circuit, which is generally of a DC-to-DC converter. FIG. 9 shows an example of configuration of such the DC-to-DC converter.
In FIG. 9, a DC voltage from a DC power source 93 is converted into an AC voltage by the use of a switching circuit 92 which is controlled by an oscillator 91. The thus converted AC voltage is amplified by an amplifier 94. Thereafter, the amplified AC voltage is stepped up by a step-up transformer 95, and rectified by a rectifying circuit 96 back into a DC voltage. whereby a higher DC voltage can be obtained.
However, a high voltage generating circuit of this type has a complicated configuration. In addition, the larger in number of conversions, the more loss of power, so that the circuit consumes more electricity.